Cold acclimation in white clover subjected to chilling and frost: changes in water and carbohydrates status
Résumé
The effect of cold acclimation on the water status and the fate of carbohydrates was studied in white clover (Trifolium repens L., cv Huia) subjected to chilling and/or freeze-thaw cycles. Treatments were applied in a controlled environment, with a constant photoperiod, for 6 weeks to plants either acclimated or non-acclimated to low temperature. Cold acclimated plants had a higher concentration of starch in the stolons at the end of the acclimation period than non-acclimated plants (54 vs. 15 mg g(-1) DW). During the experiment, the leaves of cold acclimated plants subjected to frosts maintained a higher relative water content (RWC) than did leaves of plants not acclimated for which we observed a strong dehydration of 80%. Under chilling, cold acclimated plants demonstrated an osmotic adjustment. We showed that only 30-40% of the variation of the osmotic potential was explained by variation in free sugar concentration, suggesting that compounds other than carbohydrates participated in the osmotic regulation. Chilling increased the carbohydrate content and frost decreased the starch concentration in non-acclimated plants only. We showed in white clover that the cold acclimation contributed to frost and chilling tolerance by the maintenance of the hydration of tissues. We demonstrated that osmotic adjustment was not completely explain by the accumulation of free sugars.